Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0008—Compositions of the inner liner
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/26—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers modified by chemical after-treatment
  • C08L23/28—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers modified by chemical after-treatment by reaction with halogens or compounds containing halogen
  • C08L23/283—Halogenated homo- or copolymers of iso-olefins

Definitions

• This invention relates to elastomeric compositions and processes for their preparation.
• halobutyl rubbers are much used, for example for tyre liners they do have some disadvantages. These include the difficulty of processing and more particularly obtaining a fast cure rate without causing scorching; of obtaining a satisfactory balance between the green strength (strength of uncured rubber) and the stress relaxation and of obtaining high cured adhesion onto general purpose rubber (GPR) substrates.
• GPR general purpose rubber
• US 4348501 discloses blends of a thermoplastic carboxy containing ethylene copolymer and cross-linked epichlorhydrin dispersed throughout the resin as small discrete particles. The resulting blend is processed as a thermoplastic material and is not thermoset after a curing step.
• GB 2179046 A discloses blends of different rubbers, with optionally added brominated butyl rubber and carboxylated rubbers for vibration mounts. There is no disclosure of the utility of bromobutyl and non-elastomer ethylene based polymers containing carboxy groups.
• GB 1424041 discloses a rubber containing material which has a low viscosity by the use of a compatible liquid polymer or copolymer of a diene which takes past in a curing process not employing sulphur.
• the rubber may contain a reactive halogen but the normally occuring allylic halogen of bromobutyl or chlorobutyl is not identified as a possible active group.
• the diene derieved component is liquid.
• the diene component may be copolymerised with an amonic group containing copolymer but 75% remains diene derived and there is no ethylene based monomer component.
• EP A 55 848 discloses a water absorbing rubber based composition with added thereto a cross-linked waterabsorbing resin of a polymer having at least 40 mol % of a carboxyl group containing component.
• a cross-linked waterabsorbing resin of a polymer having at least 40 mol % of a carboxyl group containing component there is no teaching of the use of the reaction of allylic halogen in, say, bromobutyl or the use of a olefin polymer with a low carboxy group content.
• GB 1096 879 suggests use (see p5 line 25) of a blend of sulphonated polymers of perfluorostyrene with other vinyl polymers.
• Page 2 line 1 indicates that the halo-substituents are not reactive. There is no teaching to use a reactive halogen containing polymer in conjunction with an olefin polymer to provide cross-linkable blend.
• US 4593062 discloses a thermoplastic mouldable composition having a continuous phase a thermoplastic material and in situ , dynamically vulcanised rubber particles containing halobutyl to give a DVA or TPO.
• the thermoplastic material is a polyolefin resin which according to a not-preferred embodiment may be a copolymer of ethylene with acrylic acid.
• the rubber also essentially contains a polychloroprene rubber.
• the proportions suggested for polychloroprene, the olefin resin and the halogenated butyl rubber are 1:1:1 (of claim 8) or from 90 to 110 wt% by reference to the polyolefin (see colum 7).
• the US 4593062 does not disclose a thermoset composition of which a minor proportion is olefinic anionic group containing copolymer nor a composition free of chloroprene or acomposition which can incorporate a cure system in a green state for subsequent curing.
• the olefin resin and halogenated butyl rubber are not intimately mixed to permit and promote their mutual cross linking and compatibility.
• a process for preparing an elastomeric composition which includes preparing a master blend of polymeric components comprising a major preparation by weight of a rubber containing reactive halogen and a minor proportion by weight of a copolymer containing anionic groups of an olefin and any fillers at a first temperature, cooling the mixture and adding a cross-linking system at a second temperature below the first and cross-linking the mixture at a third temperature above the first temperature.
• the reacting halogen may be the allylic halogen of halobutyl rubber.
• the anionic groups may be the non-neutralised and/or neutralised carboxylic acid groups of ethylene copolymers. The uncured strength of the blend is improved.
• an elastomeric composition comprising a major proportion by weight of a rubber comprising a rubber containing reactive halogen and a minor proportion by weight of polymer containing anionic groups such as a copolymer of an olefin and an unsaturated carboxylic acid.
• a rubber comprising a rubber containing reactive halogen
• polymer containing anionic groups such as a copolymer of an olefin and an unsaturated carboxylic acid.
• the polymer content of the blend consists predominently of the reactive halogen containing rubber and the olefin copolymer. This blend may be stored etc. without the presence of a cross-linking system.
• a rubber containing reactive halogen for example a least 50% by weight of halobutyl rubber.
• a major proportion of a rubber containing reactive halogen for example a least 50% by weight of halobutyl rubber.
• Advantageously substantially no non-functional olefin resin is present.
• Advantageously substantially no polychloroprene is present.
• the composition preferably is a binary blend consisting essentially -as far as polymeric components is concerned- of the halobutyl and anionic group containing polymer.
• the amounts and nature of the components of such blends should be selected to provide an intimately mixed blend without a continuous thermoplastic olefin polymer phase.
• the rubber is preferably a halobutyl rubber, i.e. a halogenated butyl rubber such as a copolymer of 70 - 95.5 % by weight of combined isoolefin having from 4 to 8 carbon atoms per molecule and 0.5 to 30 % by weight of combined multiolefin having 4 to 14 carbon atoms per molecule.
• a halobutyl rubber i.e. a halogenated butyl rubber such as a copolymer of 70 - 95.5 % by weight of combined isoolefin having from 4 to 8 carbon atoms per molecule and 0.5 to 30 % by weight of combined multiolefin having 4 to 14 carbon atoms per molecule.
• the butyl rubber from which the halobutyl rubber is derived contains 85 to 99.5 % by weight (especially 95 to 99.5 % by weight) of a C4 to C7 isoolefin, such as isobutene and 0.5 to 15% by weight (especially 0.5 to 5 % by weight) of a conjugated C4 to C10 multi-olefin.
• a C4 to C7 isoolefin such as isobutene
• 0.5 to 15% by weight especially 0.5 to 5 % by weight
• butyl-type rubbers The preparation of butyl-type rubbers is amply described an, in general, it consists of the reaction product of a C4 - C7 isoolefin (preferably isobutylene) with a C4 - C10 (preferably a C4 - C6) conjugated diolefin, such as isoprene, budadiene, dimethyl butadiene, piperylene, etc.
• a C4 - C10 preferably a C4 - C6 conjugated diolefin, such as isoprene, budadiene, dimethyl butadiene, piperylene, etc.
• the reaction product of isobutylene and isoprene is preferred.
• the preparation of butyl rubber is also described in US patent 2,356,128 which is incorporated herein by reference.
• Conventional high molecular weight butyl rubber generally has a number average molecular weight of about 25,000 to about 500,000, preferably about 80,000 to about 300,000 especially about 100,000 to about 250,000; and a Wijs Iodine No. of about 0.5 to 50, preferably 1 to 20. More recently low molecular weight polymers have also been prepared which have number average molecular weights of from 5,000 to 25,000 and unsaturation expressed as mole %, of 2-10.
• Chlorinated and brominated butyl rubber generally contain at least 0.5 weight % combined halogen and up to 1 atim of halogen per double bond in the copolymer; chlorobrominated butyl rubber generally contains from 1.0 to 3.0 weight % bromine and from 0.05 to 0.5 weight % chlorine.
• the rubber forming the major proportion by weight of the composition of this invention is a mixture of a halobutyl rubber and another rubber
• the other rubber can for example be natural rubber (NR), polybutadiene rubber or styrene - butadiene rubber (SBR).
• the halobutyl rubber When a mixture of rubbers is used the halobutyl rubber usually forms a maojor proportion by weight of the mixture, for example 50 to 80 weight %, e.g. about 60 weight %.
• the copolymer is derived from olefin (with which term generally mono-olefins are indicated) and an unsaturated carboxylic acid.
• the olefin is preferably of low molecular weight and C2 to C5 olefins are useful. Particularly preferred olefins are propylene and especially ethylene.
• the unsaturated carboxylic acid is preferably an ethylenically unsaturated carboxylic acid and should contain one or more double bonds. It may be a polycarboxylic acid, e.g. an alpha-beta ethylenically unsaturated carboxylic acid preferably containing 4 to 8 carbon atoms e.g. 4 to 6 carbon atoms per molecule, such as maleic acid, fumaric acid or itaconic acid. Preferably however, it is a monocarboxylic acid, e.g. an alpha-beta ethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms e.g.
• Acrylic acid is the most preferred acid.
• the copolymer has at least 50 mole % of olefin e.g. 60 to 80 % mole of olefin.
• the number average molecular weight of the ethylene-acrylic acid copolymers is typically between 500 and 5000, e.g. 1500 to 4000, the acid number between 10 and 200, preferably 20 to 130 mgKOH/g and the density between 0.91 and 0.95 usually between 0.925 and 0.945.
• the Vicat softening point of the copolymers is usually between 55° and 90°C and the melting point between 85° and 110°C.
• the melt index determined by ASTM method D-1238 is usually 1 to 100 g/10 minutes, e.g. from 1.5 to 8.5 g/10 minutes for ethylene/acrylic acid copolymers and from 1.0 to 6.0 g/10 minutes for ethylene/methacrylic acid copolymers, the value increasing with increasing ethylene content.
• a preferred copolymer of ethylene and acrylic acid has the following properties: Melt index : 8.0 g/10 min Density : 0.931 g/cm3 Acid number : 43 mgKOH/g Melting point : 103°C Vicat softening point : 86°C Tensile at break : 16.5 MPa Elongation at break : 600% E modulus : 186 MPa Dart impact strength * : 300gF50 * 50 micron film 2.2:1 blow up ratio.
• the copolymers are usually prepared by polymerising the monomers in the vapour phase at high pressure, usually 1500 to 2500 bars, at a temperature usually between 150°C and 250°C preferably between 190'C and 220°C, using a free radical initiator.
• Suitable initiators are peroxyesters such as peroxypivalates, peroctoates or perbenzoates or a mixture of these or peroxides.
• the polymerisation reaction can be continuous and the product can be continually withdrawn from the reactor as it is formed.
• the viscosity of the product is controlled by using a transfer agent such as isobutylene.
• a transfer agent such as isobutylene.
• Other suitable transfer agents are compounds such as an alcohol, a ketone, an aldehyde or an aliphatic or aromatic hydrocarbon.
• the weight ratio of olefin copolymer to rubber comprising halobutyl rubber is between 40:60 and 5:95 preferably between 25:75 and 10:90 especially about 15:85.
• composition of this invention in a usable form, for example as a sheet or a slab, it is desirable that the copolymer and rubber comprising halobutyl rubber be submitted to high shear mixing generally without a cross-linking/vulcanising system.
• This can be achieved by introducing the blend of rubber and copolymer into a mixer such as an internal mixer or a Banbury mixer. The blend is then subjected to thorough mixing.
• additives or fillers it is usual to add one or more additives or fillers to the mixture of rubber and copolymer.
• additives with typical amounts (in parts by weight based on 100 parts by weight of rubber plus copolymer) are carbon black (e.g. GPF, HAF) 40 to 70 e.g. 50, oil (e.g. naphtenic oil Flexon 580 or paraffinic oil Flexon 876 or aromatic oil Dutrex R) 5 to 10 e.g. 7 to 8; stearic acid, 0.5 to 1.5, e.g. 1.0.
• the curing/vulcanising system components may include zinc oxide 1 to 10 e.g. 3; sulphur 0.1 to 1.0 e.g.
• MBTS mercapto benzo thiazyl disulphide
• the zinc oxide, sulphur, MBTS and zinc stearate constitute only one of the cure systems which may be used in practice. Other cure system variations are possible.
• the cure system incorporates a neutralising agent which can help to form ionomers and also contributes to linking of the copolymer and the rubber.
• composition of the invention in as for example a sheet, after mixing thoroughly with or without additives in the mixer, it can be extruded or calendered. The sheet thereby obtained is still in the green or uncured state. The addition of the acid group containing polymer appears to help in avoiding premature undesirable curing.
• the composition thereby obtained has the following advantages over pure halobutyl rubber: Mooney Scorch much improved especially in the case of chlorobutyl; the T90 technical cure time is shortened by nearly 25 % at 150°C, the green strength is increased (highest modulus of elasticity), hardness and particularly hot modulus as shown on the rheographs; and very importantly there is better adhesion to an elastomer e.g. general purpose rubber.
• this invention also provides the use of a composition having good adhesion to an elastomer, said composition comprising an intimately mixed blend of a major proportion by weight of a rubber comprising a halobutyl rubber and a minor proportion by weight of a copolymer of an olefin and an unsaturated carboxylic acid.
• this invention provides an elastomeric composition
• an elastomeric composition comprising an elastomeric substrate supporting an intimately mixed blend of a major proportion by weight of a rubber comprising a halobutyl rubber and a minor proportion by weight of a copolymer of an olefin and an unsaturated carboxylic acid, said substrate and said blend having been co-covulcanised.
• the elastomeric substrate can comprise any rubber or mixture of rubbers, but is preferably general purpose rubber, e.g. natural rubber polybutadiene rubber, styrene - butadiene rubber, carboxylated styrene-butadiene rubber, carboxylated styrene-butadiene rubber, polyisoprene rubber, acrylonitrile-butadiene - styrene rubber or any mixture thereof.
• general purpose rubber e.g. natural rubber polybutadiene rubber, styrene - butadiene rubber, carboxylated styrene-butadiene rubber, carboxylated styrene-butadiene rubber, polyisoprene rubber, acrylonitrile-butadiene - styrene rubber or any mixture thereof.
• the substrate is the carcass of a tyre and the blend is the tyre inner liner.
• the carcass is usually natural rubber or a blend of natural rubber and styrene-butadiene rubber (SBR).
• SBR styrene-butadiene rubber
• the carcass and inner liner and other components e.g. tread, sidewall, beads
• the "green" (uncured) tyre is passed to a curing press where the tyre is vulcanised. This is achieved by raising the temperature of and increasing the pressure on the tyre.
• the temperature is 120°C to 200°C, e.g. about 150°C and the pressure is 1 to 10 Pa e.g. about 5 Pa.
• the curing time is typically 15 min to 1 hour, for example about 30 minutes.
• the modulus of elasticity, and tensile strength are strongly improved, particularly with chlorobutyl.
• the basic cured adhesion i.e. a measure which takes account of difference in modulus of halobutyl compounds
• the blend responds to cure system chemicals in the same overall manner as natural rubber, so facilitating optimisation of process conditions. Whilst the green strength is higher, the fast stress decay or low elastic memory improves processing and product quality.
• chlorobutyl rubber Chlorobutyl 1066 of Exxon Chemical Company
• bromobutyl rubber Bromobutyl 2222 of Exxon Chemical Company
• the ethylene copolymer contained 94 weight % of ethylene units and 6 weight % of acrylic acid units. Its other properties were as follows: Property Unit ASTM Method Value Melt index g/10 min D1328 8.0 Density g/cm3 D792 0.931 Acid number mg/KOH/g - 47.0 Melting point °C DSC* 103.0 Vicat softening point °C D1525 86.0 Tensile at break MPa D638 17.0 Elongation at break % D638 600.0 E-Modulus MPa D638 186.0 Dart impact strength** gF50 D1709 300.0 Haze** % D1003 5.0 Gloss** % D2457 9.5 * Differential scanning calorimeter ** 50 micron film 2.2:1 Blow-up ratio.
• composition (in parts by weight) of the four blends A, B, C and D were as follows: A B C D Chlorobutyl rubber 100 100 - - Bromobutyl rubber - - 100 100 Ethylene Copolymer - 15 - 15 GPF N-660 50 50 50 50 50 Flexon 876 8 8 8 8 Stearic acid 1 1 1 1 1 Zinc oxide 3 3 3 3 Sulphur 0.5 0.5 0.5 0.5 0.5 MBTS 1.5 1.5 1.5 1.5 Zinc stearate 2 2 2 2 2 2 2 2 2 2 2 2 2
• the four blends were each thoroughly mixed in a small Banbury mixer. For the first 1.5 minutes the halobutyl rubber, one third the carbon black and all the ethylene copolymer were mixed. The remainder of the carbon black was then added and the paraffinic oils and all the other additives were added and the mixing continued for another 2.5 minutes until a temperature of 140°C was reached. The blends were then dumped and cooled down.
• the blends were then reintroduced into the mixer, the zinc oxide, sulphur, MBTS and zinc stearate were added and the compounds were mixed and dumped at 90°C.
• blends were placed in a mould and cured at a temperature of 180°C for 15 minutes under pressure.
• the Mooney viscosity, stress relaxation, green strength and self-tack relate to the uncured blends and the other data relate to the cured blends.
• blends B and D show advantages over respectively A and C in terms of scorch/cure time balance, improved modulus and tensile strength, green strength and stress relaxation rate, improved "true” or basic adhesion to HR or HR/SBR substrates. This indicates the advantage of the inclusion of the ethylene copolymer in the blends.
• An elastomeric blend H was prepared by mixing in a Banbury mixer 60 parts by weight of the chlorobutyl rubber used in Example 1, 40 parts by weight of natural rubber, 70 parts by weight of GPF carbon black, 50 parts by weight of whiting, 12 parts by weight of paraffinic oil Flexon 876, 1 part by weight of stearic acid, 3 parts by weight of zinc oxide, 1 part by weight of Vultac (an alkyl phenol disulphide curing agent), 1 part by weight of MBTS and 2 parts by weight of zinc stearate.
• Blends E, F and G were prepared and these were the same as blend H except that respectively 5, 10 and 15 phr (parts by weight per hundred parts by weight of halobutyl plus natural rubber), of the ethylene copolymer used in Example 1 were also added.
• Two other blends I and J were also prepared, these being the same as blend H except that respectively 0.2 and 0.5 phr (parts by weight per hundred parts by weight of chlorobutyl plus natural rubber), of magnesium oxide (Maglite D) were also added.
• blends E, F, G, H, I and J were press-cured at-180°C for 8 minutes (blends E, F and G) 7 minutes (blend H) and 15 minutes (blends I and J).
• Blends K, L, M were prepared as follows: K L M Chorobutyl 1066 100 100 100 Carbon black GPF 50 50 50 Flexon 876 8 8 8 Stearic acid 1 1 1 Polyethylene MI 709/10 min 00.913 10 - - Escor TR 5000 - 10 - Escor TR 5100 (MI 8,9% AA) - - 10 (all units are in parts by weight)
• Blends M and L provide an improved Hardness modulus and Tensile Strength over blend K, illustrating that it is not merely the presence of an olefinic backbone chain which creates the improved products of the invention.

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Citations (2)

• 1988
  • 1988-07-08 GB GB888816310A patent/GB8816310D0/en active Pending
• 1989
  • 1989-07-06 DE DE68926188T patent/DE68926188T2/de not_active Expired - Fee Related
  • 1989-07-06 AT AT89306888T patent/ATE136569T1/de not_active IP Right Cessation
  • 1989-07-06 ES ES89306888T patent/ES2085278T3/es not_active Expired - Lifetime
  • 1989-07-06 EP EP89306888A patent/EP0350312B1/fr not_active Expired - Lifetime
  • 1989-07-07 BR BR898903375A patent/BR8903375A/pt unknown
  • 1989-07-10 JP JP1177849A patent/JPH02103235A/ja active Pending

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